1. Technical Field
The present invention relates generally to differentials for use in the driveline of a motor vehicle. In particular, the present invention is directed to a differential assembly having a differential case with laser hardened gear pockets.
2. Discussion
As is known, motor vehicles have driveline systems equipped with differentials which function to accommodate rotary speed differences between two rotary components such as, for example, a pair of axle shafts. Most typically, the differential includes a differential case, a pair of output shafts, and a gearset mounted in the differential case that is operable for transferring rotary power (i.e., drive torque) from the differential case to the output shafts while permitting speed differentiation between the output shafts. In parallel-axis helical differentials, the gearset includes a pair of side gears fixed for rotation with the output shafts and two or more sets of meshed pinion gears mounted in gear pockets formed in the differential case. In particular, each set of pinion gears includes a first pinion rotatably mounted in a first gear pocket and which is meshed with a second pinion gear rotatably mounted in a second gear pocket. The first pinion gear is also meshed with one of the side gears while the second pinion gear is meshed with the other side gears. The gear pockets extend longitudinally and are circumferentially arranged such that each pinion gear may rotate about its own axis parallel to the rotary axis of the differential case and the output shafts. When speed differentiation occurs between the output shafts, each pinion gear rotates about its own axis and is thrust into frictional engagement with the inner wall surface of the gear pocket to generate a differential limiting force. By way of example, a conventional differential assembly of the type disclosed is shown in U.S. Pat. No. 5,556,351.
In order to reduce wear between the pinion gears and the wall surface of the gear pockets, various surface hardening techniques have been employed. Most commonly, the gear pockets in the differential case are carburized or induction hardened. As is known, such localized surface hardening processes require that certain portions of the differential case must be masked to avoid hardening. Moreover, the subsequent quenching operation may cause the differential case to distort, which will then invariably require a final grinding operation to correct the distortion. It will be appreciated that use of the carburizing method to harden differential cases is both energy and labor intensive and, therefore, is quite expensive. In addition, the carburizing process requires a large amount of equipment including a furnace, custom quenching dies for each differential case, masking equipment, and grinding equipment.
Therefore, it would be desirable to provide a method for hardening the gear pockets and/or other portions of a differential case which is less expensive and time-consuming than prior art surface hardening methods.